The present invention concerns an uncoupling device for a timepiece mechanism, comprising two coaxial wheels that can be coupled with each other in rotation in at least one direction via respective coupling elements arranged on opposite flanks of said wheels, wherein one of the coaxial wheels, called the coupling wheel, is mobile in the axial direction and is biased by a return spring, which tends to mesh the coupling elements. The invention also concerns a watch movement that includes this type of device, particularly in an automatic winding mechanism.
In most current automatic winding mechanisms, the direction reverser device is formed by a pair of unidirectional coupling wheels arranged in parallel, for example wheels with rollers or clicks. The mainspring, in its wound state, rests on the reduction train, tending to rotate it in the opposite direction to the winding direction, but the reverser device locks this reverse rotation, thus preventing the mainspring from letting down like the retaining click that acts on the barrel ratchet in manually wound movements. This click is nonetheless retained in most automatically wound calibres to prevent the spring letting down when the automatic winding module is removed, but it has the drawback of causing a waste of energy during winding. This is why it tends to be omitted when the reverser device of the automatic winding mechanism can prevent the barrel from letting down.
However, it is then useful to provide an uncoupling device in the automatic winding train, to enable a watchmaker to let the barrel down manually, particularly when he is dismantling part of the movement. Further, this device is generally arranged so that it is automatically uncoupled when the barrel is wound manually, to avoid making the first elements of the automatic winding train rotate at high speed. The uncoupling may be lateral or vertical, depending upon the direction of movement of the mobile coupling device.
The uncoupling device is usually of the lateral type, wherein the coupling element moves laterally relative to the arbours of the automatic winding train. This mobile element is an intermediate wheel, which, in order to be released from the ratchet or an intermediate drive wheel of the ratchet, is carried by a lever associated with a manual control and a return spring. In some cases, the use of this type of lever system can create difficulties in the design of a watch movement, particularly from the point of view of lateral space requirement or the arrangement of pivots.
Another type of lateral uncoupling device uses a jumper spring, carried by a wheel and applied to the tip of the teeth of a star type toothed wheel. CH Patent No. 655221 illustrates the use of this type of device in combination with a second time zone indicator and the associated corrector device. The use of this type of jumper spring cannot be envisaged in an automatic winding train, since it would be too difficult to control manually.
CH Patent No. 352624 discloses a vertical type uncoupling device, i.e. that one that moves perpendicularly to the bottom plate of the movement, in combination with two types of automatic winding mechanisms. The vertical arbour of the uncoupling device is carried in a conventional manner by jewels in the bottom plate and the barrel bar. It carries the last wheel of the reduction gear, which has a Breguet toothing on the top surface thereof. Above the Breguet toothing, the coupling wheel provided with a corresponding Breguet toothing can rotate and slide on the vertical arbour and remains permanently meshed with an intermediate wheel engaged on the barrel ratchet. The coupling wheel further includes an hour wheel with a circular external groove. A tipping control lever, which ends in a fork, engaged in said circular groove, is stressed by a return spring to keep the Breguet toothings coupled or return them to a coupled position. By acting on the other end of this lever, the watchmaker can cause uncoupling to occur in order to let down the barrel. During manual winding, the Breguet toothings become uncoupled by themselves by overcoming the effect of the return spring.
A considerable drawback of the aforementioned design lies in the resistant torque caused by friction of the control lever in the groove of the coupling wheel, since this friction is exerted at some distance from the axis of rotation. Added to this is the requirement for careful lubrication. Another drawback is that the uncoupling device arbour occupies the entire top space comprised between the bottom plate and the barrel bar, preventing any other element from occupying part of this top space. Finally, the control lever and the attachment thereof to the bottom plate occupy space next to the uncoupling device.